Correction: This article has been updated to reflect the following correction. D.C. Police Officer Emmanuel Smith said he used his weapon to provide "cover" for colleagues helping a wounded colleague. He did not say he fired his weapon, as the article previously stated.

Officer Vernon Dallas, center, holds the Specialized Unit of the Year award. He and six others received the award for their work to end the Navy Yard crisis. (Sarah L. Voisin/The Washington Post)

They couldn’t see Aaron Alexis, but they could hear him shooting.

So D.C. police officers Dorian DeSantis, Scott Williams and Emmanuel Smith followed the sounds of gunfire down a long corridor deep inside Building 197 at the Washington Navy Yard, past row upon row of identical, government-issued cubicles.

Almost at the end of a corridor, Smith, 46, heard gunfire and saw Williams fall, struck by bullets in each leg. Smith, who was armed with an AR-15 assault rifle, said he provided cover as two more responders, Brian Kelley and Ed Martin of the Naval Criminal Investigative Service, dragged Williams to an entrance and then carried him on their backs down two flights of stairs.

The account, offered in interviews and speeches Wednesday at an awards ceremony for the officers who responded to the Sept. 16 incident, offers new details of the heroism displayed during the mass shooting that left 12 people dead. During the program, DeSantis, who ultimately fired the shots that killed Alexis, was named officer of the year by the nonprofit Police Foundation, which raises money for programs and recently paid for a new training center. These officers and others were also honored by the police department in February.

Smith, in an interview, recounted the harrowing moments as the trio chased the sound of gunfire on the building’s third floor. His group was among the last to go inside and join the hunt for Alexis, nearly an hour into the siege. Police have said that 10 of the 12 people killed were dead within the first six minutes. Neither DeSantis nor Williams, who embraced each other after being honored, spoke at the event or to a reporter afterward.

The FBI released video of shooter Aaron Alexis walking inside Navy Yard with a gun on the day of the shooting. (Thomas LeGro/The Washington Post)

Smith said they couldn’t see above the 6-foot-high partitions but kept walking through the maze of desks. He said he heard two shots, whirled and saw Williams fall. “We never saw Alexis,” Smith said.

As the Naval officers dragged Williams back toward a door, Smith said, he stepped into an opening to guard them. Although the 24-year veteran recalled hearing only two shots, he said he later learned that Alexis had fired six or seven times at him and the others.

D.C. Police Chief Cathy L. Lanier described a nearly impossible engagement in a maze of cubicles and hallways that officers had to navigate to find Alexis in a building she said he could have hid in for days. He was armed with a Remington shotgun and a handgun he stole from a retired Maryland State Police trooper who was a security guard in the building.

“The tactical disadvantage they had, it really was an invisible fight,” Lanier said, noting that 117 officers from her force and others streamed into the building during the incident, which lasted just over an hour.

Lanier said 160 cameras recorded the shooting spree and “captured every move of Aaron Alexis and the officers who entered the building. Many officers never even saw the man they were hunting. What a nightmare it must have been for them,” Lanier said.

The chief said that by the time DeSantis confronted Alexis, a 34-year-old Naval contractor who authorities said believed he was being controlled by low-frequency radio waves — the two were standing nearly face-to-face. Both opened fire, and Lanier said DeSantis didn’t know he was shot until he found a round lodged in his protective vest the next day.

Speaking at the Arena Stage at the Mead Center for American Theater, where the ceremony was held, Lanier said the shooting spree and police response has altered the way her department trains for such incidents, and the department has said a report will be made public when the investigation has concluded.

The chief praised the seven officers who first went into Building 197, encountered the body of the state trooper and found themselves in an atrium with no cover. They overturned furniture to protect themselves, took the key card off the security guard to open locked doors and remembered to prop them open for officers that followed through the 630,000-square-foot expanse with more than 30,000 office cubicles.

“That is not easy to do,” Lanier said, “when you’re after somebody who is shooting at you. . . . They went directly toward where the gunfire was coming from, knowing they would encounter Alexis at some point.”

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